II. Physiology: Parathyroid Hormone (PTH)

  1. Images
    1. CalciumHomeostasis.png
  2. Anatomy
    1. Four small Parathyroid Glands are found at the posterior aspect of Thyroid Gland
  3. PTH is released by Parathyroid Glands in neck in an inverse relationship to Serum Calcium levels
    1. Parathyroid Glands increase PTH secretion with Hypocalcemia (Low Serum Calcium)
    2. Parathyroid Glands decrease PTH secretion with Hypercalcemia (High Serum Calcium)
  4. Pharmacokinetics
    1. PTH is an 84 amino-acid peptide produced and secreted by the Parathyroid Glands
    2. Parathyroid Glands respond to Hypocalcemia or Hypercalcemia within minutes of out-of-range Serum Calcium
    3. Parathyroid Glands hypertrophy in response to sustained Hypocalcemia
    4. Parathyroid production and secretion of PTH
      1. Suppressed by negative feedback from increased Serum Calcium and 1-25 dihydroxyvitamin D
    5. Circulating half-life: 2-5 minutes
    6. Metabolized by liver and Kidney
  5. Mechanism
    1. See Calcium Homeostasis
    2. PTH stimulates Osteoclasts in bone
      1. Osteoclasts mobilize bone Calcium
      2. Phosphates are also mobilized by bone, but with increased renal phosphate excretion
    3. PTH acts at Kidneys to increase Serum Calcium
      1. Increases Calcium reabsorption
      2. Kidney activates 25-hydroxyVitamin D
        1. Converts it to 1,25-dihydroxyVitamin D3
        2. Increases Calcium and phosphate via intestinal and renal absorption and bone mobilization

III. Labs

  1. Tests to avoid
    1. C-Terminal PTH
    2. N-Terminal PTH
  2. Recommended Test
    1. Whole Molecule PTH by IRMA (Mid-region or Intact PTH)
      1. Measures C-Terminal and N-Terminal PTH

IV. Interpretation: Normal Serum Calcium

  1. Parathyroid Hormone: 10 to 66 pg/ml
    1. Normal Parathyroid Function

V. Interpretation: High Serum Calcium

  1. Parathyroid Hormone >66 pg/ml
    1. Primary Hyperparathyroidism
    2. Consider MEN I or MEN II
  2. Parathyroid Hormone 10-66 pg/ml
    1. Familial Hypocalciuric Hypercalcemia
      1. 24 hour Urine Calcium to Creatine clearance <0.01
  3. Parathyroid Hormone <10 pg/ml
    1. Parathyroid Cancer
    2. Granulomatous Disease
    3. Milk-Alkali Syndrome
    4. Adrenal Insufficiency
    5. Hyperthyroidism
    6. Prolonged immobilization
    7. Medication related
      1. Lithium
      2. Theophylline
      3. Tamoxifen

VI. Interpretation: Low Serum Calcium

  1. Parathyroid Hormone >66 pg/ml
    1. Secondary Hyperparathyroidism
      1. Renal Failure
      2. Gastrointestinal malabsorption
      3. Hypomagnesemia
  2. Parathyroid Hormone 10 to 66 pg/ml
    1. Pseudohypoparathyroidism
  3. Parathyroid Hormone <10 pg/ml
    1. Hypoparathyroidism

VII. References

  1. Bakerman (1984) ABCs of Lab Data, ILD, Greenville, NC
  2. Einhorn (2001) CMEA Medicine Lecture, San Diego
  3. Taniegra (2004) Am Fam Physician 69(2):333-40 [PubMed]

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Related Studies

Ontology: Parathyroid Hormone (C0030520)

Definition (MSH) A polypeptide hormone (84 amino acid residues) secreted by the PARATHYROID GLANDS which performs the essential role of maintaining intracellular CALCIUM levels in the body. Parathyroid hormone increases intracellular calcium by promoting the release of CALCIUM from BONE, increases the intestinal absorption of calcium, increases the renal tubular reabsorption of calcium, and increases the renal excretion of phosphates.
Definition (CSP) polypeptide hormone secreted by the parathyroid glands which maintains intracellular calcium levels in the body; parathyroid hormone increases intracellular calcium by promoting the release of calcium from bone, increases the intestinal absorption of calcium, increases the renal tubular reabsorption of calcium, and increases the renal excretion of phosphates.
Definition (PDQ) Encoded by human PTH Gene (Parathyroid Hormone Family), secreted (parathyroid cells) 115-aa 13-kDa (precursor) Parathyroid Hormone elevates blood Ca2+ levels by dissolving the salts in bone and preventing renal excretion. PTH defects cause familial isolated hypoparathyroidism. (NCI) Check for "http://www.cancer.gov/Search/ClinicalTrialsLink.aspx?id=489119&idtype=1" active clinical trials or "http://www.cancer.gov/Search/ClinicalTrialsLink.aspx?id=489119&idtype=1&closed=1" closed clinical trials using this agent. ("http://nciterms.nci.nih.gov:80/NCIBrowser/ConceptReport.jsp?dictionary=NCI_Thesaurus&code=C41027" NCI Thesaurus)
Concepts Hormone (T125) , Amino Acid, Peptide, or Protein (T116) , Pharmacologic Substance (T121)
MSH D010281
SnomedCT 27518004, 68136009, 4076007, 373752003
LNC LP18184-9, MTHU005026
English Hormone, Parathyroid, Parathormone, Parathyrin, Parathyroid Hormone (1-84), PTH (1-84), PTH, parathyroid (medication), parathyroid, Parathyroid Hormone, Parathyroid Hormone [Chemical/Ingredient], parathyrin, parathormone, parathyroid hormones, PARATHYROID HORMONE, parathyroid hormone, Parathormone (substance), Parathyroid Hormones, Parathyroid hormone, PTH - Parathyroid hormone, Parathyroid hormone preparation, Parathormone preparation, Parathyroid extract, Parathyroid hormone agent (substance), Parathyroid hormone agent, Parathyroid hormone preparation (product), Parathormone preparation, NOS, Parathormone, NOS, Parathyroid extract, NOS, Parathyroid hormone preparation, NOS, Parathyroid hormone, NOS, Parathyroid hormone preparation (substance), Parathyroid, Parathyroid hormone (substance), Intact parathyroid hormone (substance)
Spanish hormona paratiroidea intacta, preparado con PTH, preparado con hormona paratiroidea (producto), hormona paratiroidea (producto), preparado con hormona paratiroidea, parathormona, parathormona (concepto no activo), agente con hormona paratiroidea (sustancia), agente con hormona paratiroidea, extracto paratiroideo, hormona paratiroidea (sustancia), hormona paratiroidea, preparado con paratohormona, preparado de PTH, preparado de hormona paratiroidea (producto), preparado de hormona paratiroidea (sustancia), preparado de hormona paratiroidea, preparado de paratohormona, Hormona Paratiroidea
Swedish Bisköldkörtelhormoner
Czech parathormon, parathyroidní hormon
Finnish Lisäkilpirauhashormoni
French Parathyrine, PTH (Parathyroid hormone), PTH (1-84), Hormone parathyroïdienne, Parathormone
German PTH (1-84), Parathyrin, Parathormon, Nebenschilddrüsenhormone
Japanese 上皮小体ホルモン, パラソルモン, 副甲状腺ホルモン
Italian PTH (1-84), Paratormoni, Ormoni paratiroidei (1-84), Paratirine, Ormoni paratiroidei
Polish Hormon przytarczyc, Parathormon, Paratyreoidyna, Hormon gruczołów przytarczycznych
Norwegian Paratyreoideahormon, PTH, Parathormon, Parathyrin, Biskjoldkjertelhormon
Portuguese Hormônio Paratireoidiano, Hormônio Paratireóideo